1. Field of the Invention
The present invention relates to an optical resolution method of (.+-.)-3,4-dihydroxybutanoic acid and to a method for producing optically active 3-hydroxy-.gamma.-butyrolactone using optically active 3,4-dihydroxybutanoic acid preferably produced by the aforementioned optical resolution method. Optically active 3-hydroxy-.gamma.-butyrolactone produced by the present invention can readily be introduced into various optically active substances useful as raw materials for the synthesis of pharmaceutical agents, such as optically active 3-hydroxytetrahydrofuran, optically active 4-hydroxypyrrolidinone, optically active 3-hydroxypyrrolidine and optically active 1-amino-2,3-dihydroxypropane, and is a compound of importance as a chiral synthon. For example, optically active 3-hydroxytetrahydrofuran obtained by reducing optically active 3-hydroxy-.gamma.-butyrolactone is useful as a raw material for the synthesis of an HIV protease inhibitor, VX-478 (see J. Am. Chem. Soc., Vol. 117, page 1181 (1995) and WO 94/05639 both incorporated herein by reference).
2. Discussion of the Related Art
The following methods for producing optically active 3,4-dihydroxybutanoic acid are known: (1) a method comprising oxidizing an optically active glucose source (Japanese Patent Laid-open No. Hei 4-338359); (2) a method comprising reducing optically active malic acid derivatives (Japanese Patent Laid-open Nos. Hei 4-149152 and Hei 6-172256); and (3) a method comprising optically resolving (.+-.)-3,4-dihydroxybutanoic acid using brucine (see J. Am. Chem. Soc., Vol. 42, page 2314 (1920) and Optical Resolution Procedures for Chemical Compounds, Vol. 2, Acids Part I, page 83 (Optical Resolution Information Center)).
However, method (1) requires the removal of by-product glycolic acid, generated together with optically active 3,4-dihydroxybutanoic acid, by silica gel chromatography. With method (2), optically active malic acid (raw material) and sodium borohydride (reducing agent) are expensive. Method (3) uses brucine (an alkaloid) as a resolving agent, which is hardly available at low cost, and therefore, the method is not suitable as an industrial process.
Hence, a method for optically resolving the raw material (.+-.)-3,4-dihydroxybutanoic acid with a readily available resolving agent at low cost is currently in demand.